Hi. I just got 2003 Surveyor travel trailer. I have watched many youtube videos on how to do this. I drained the hot water tank and left the plug out. My hotwater tank has only one by-pass valve so I guess it must have a check valve on the hot outlet side. I made a hose to attach to the inlet side of the pump to suck in the antifreeze. I pump and the antifreeze is just going out through the tank. Frustrating.

I initially thought I had a frozen line but it is only the hot water tabs that aren't flowing.

I think: 1. the one valve you have is bad/in the wrong position, 2. you're either not closing a valve (would the cold water feed to the water heater), or 3. there's a check valve on the hot water out from the water heater that is failing to close.